1. Field of the Invention
The present invention relates to a device for detecting failures in a communication network of an automotive vehicle, in which plural electronic control units (ECUs) are connected to one another through communication lines.
2. Description of Related Art
Recently, various network systems for use in an automobile, such as CAN (control area network), have been developed. Plural ECUs are interconnected in such a network, and it is required to detect communication failures in the network. Various systems for detecting the communication failures are proposed. For example, JP-A-8-500707 discloses a system in which situations where an ACK message (a message acknowledging receipt of information sent from a sender) is not sent back to a sender are found out, and failures in the network are determined based on such findings. If the communication line in the network is damaged, for example, the ACK message is not sent back to the sender. The failures in the communication line are detected by monitoring the ACK message.
In recent automobile networks, a number of communication modules are connected through a common communication line to handle an increased amount of information and data, and data communication among plural modules is performed. Examples of such networks are briefly shown in FIGS. 6A and 6B. In an example shown in FIG. 6A, an ECU 31 having a communication module 31a is connected to plural ECUs 32, 33 each having each communication module 32a, 33a through a communication line 34. In an example shown in FIG. 6B, an ECU 41 having plural communication modules 41a, 41b is connected to an ECU 42 having a communication module 42a through a communication line 43.
In the network shown in FIG. 6A, if the ECU 32 becomes unable to send back an ACK message to the ECU 31 due to its failure, another ECU 33 sends an ACK message to the ECU 31 in place of the ECU 32 through a dotted line. Therefore, the ECU 31 cannot detect the failure occurred in the ECU 32 according to the conventional failure detection method. In the network shown in FIG. 6B, if the communication line 43 is discontinued, the ACK messages are exchanged between the communication modules 41a and 41b because they are interconnected in the ECU 41. Therefore, the ECU 41 is not able to detect the communication line failure.